An information input device has been heretofore known which comprises a combination of an input pen as a coordinate indication means, a tablet comprising a transparent coordinate input board for placing the input pen in contact and a coordinate detection board for detecting a coordinate with which the input pen contacts by an electrostatic capacity coupling system or an electromagnetic induction system, a CRT for placing the tablet thereon, a display unit such as a liquid crystal display unit, and an arithmetic portion for calculating the contact coordinate of the input pen with the transparent coordinate input board. According to the aforementioned device, a nib of the input pen is placed in contact with the surface of the transparent coordinate input board (that is, a coordinate input surface) to thereby detect a signal of the coordinate detection board, a contact position of the input pen with the coordinate input board is calculated from the thus detected signal and then outputted to a host computer.
In the above-described information input device, the nib of the input pen is normally formed of a conductive material such as stainless steel iron or the like. On the other hand, it is also known that the tip portion of the nib is coated with a high polymer molecule in order to prevent the coordinate input surface with which the nib contacts from being scratched, to satisfy the electrostatic pressure resistance, and to enhance a touch (a so-called writing feeling) at the time of contact of the nib of the input pen with the coordinate input surface as disclosed in Japanese Patent Application Laid-Open No. 61-183727.
Further, in the aforementioned device, the tablet comprises the transparent coordinate input board and the coordinate detection board. The transparent coordinate input board is generally made of glass in consideration of transparency and strength, but may be formed from a plastic plate or one obtained by sticking a plastic film or the like to glass. Further, there is also known a tablet having a coordinate input surface subjected to nonglaring treatment in order to enhance the visibility of characters or figures displayed on the display unit.
In the case where the tablet is placed on the display unit, not only the coordinate input board but also the coordinate detection board need be transparent. In this case, use is made of the coordinate detection board in which a plurality of transparent electrode wires in directions of axes X and Y are arranged on a transparent substrate. The transparent electrode wires are formed of indium oxide (hereinafter referred to ITO) and tin oxide, and the transparent substrate is made of glass or the like (see FIG. 2). It is to be noted that when the tablet is used in such a manner as described, the coordinate input board is often made integral with the coordinate detection board.
It is further known that a display unit such as a liquid crystal is arranged under a transparent coordinate input board of the tablet and a coordinate detection board is arranged under the display unit (see FIG. 3).
However, the nib having its tip portion merely coated with an organic high polymer molecule as in the above-described input pen has a problem in that particularly when the nip is placed in contact with the coordinate input board having the coordinate input surface subjected to nonglaring treatment, it is insufficient to absorb a rugged feeling of the coordinate input surface, failing to obtain a good writing feeling. For example, when the nib coated with an organic high polymer molecule material with less elasticity is used, the press force thereof at the time of contact is applied as a load to an operator to bring forth a fatigue. Further, a nib coated with a material having an excessively high hardness has a drawback such that an abnormal sound occurs at the time of sliding thereof relative to the coordinate input surface, and the touch is so hard that characters or figures are difficult to be written. Conversely, a nib coated with a material having an excessively low hardness has a problem such that when the input pen is placed in contact with the coordinate input surface, a portion of the nib coated with a high polymer molecule is sometimes deviated so that an input coordinate position is difficult to be designated, and that also at the time of sliding thereof relative to the coordinate input surface, a feeling of unrest occurs due to an occurrence of deviation of a portion coated with a high polymer molecule similar to the case where the nib is placed in contact. Moreover, there are problems in that in the case where a friction between the nib and the coordinate input surface is too small, the nib slips at the time of designation of an input coordinate position so that an erroneous input tends to occur, whereas in the case where the friction is too large, the nib is caught at the time of sliding thereof relative to the coordinate input surface, and an operator feels fatigue in use thereof for a long period of time.
Furthermore, the transparent coordinate input board has a problem in that a degree of non-glaring treatment influences on a writing feeling of an input pen, and a problem in that an image on the display unit is hard to see .
There is a further problem in that in the case where the coordinate detection board is placed on the display unit for use, a difference between transmittance and color tone of portions where transparent electrode wires are present and transmittance and color tone of portions where transparent electrode wires are not present becomes large due to the transparent electrode wires arranged on the transparent substrate and, as a result, lattice stripes caused by a plurality of electrode wires in directions of axes X and Y appear to disturb the visibility of a display image plane of the display unit.